This invention relates to an electrophotographic printing machine and more particularly to a multifunction erase lamp system which incorporates addressable segments for accomplishing interdocument and edge erase functions, vertical image shifts and improved turn on response.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational area contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith.
In this process, certain areas of the photoconductive member are charged and not used for imaging. These charged, unused areas are subsequently developed with toner particles. Inasmuch as these toner particles are not transferred to the copy sheet, they must be cleaned from the photoconductive member prior to the next successive imaging cycle or they will degrade the copy. Alternatively, if these non-image regions are not charged, or if they are discharged before development, the non-image areas of the photoconductive member will not be developed with toner particles and there is no requirement to clean the photoconductive member. The non-image areas on the photoconductive member requiring discharge are the interdocument area and the edge areas. The interdocument areas are the non-image areas before the first electrostatic latent image, between adjacent latent images, and after the last latent image of a series of latent images recorded on the photoconductive member. The edge areas are the non-image areas adjacent the sides of the latent image recorded on the photoconductive member. If the original document is edge registered, then one edge of the latent image will always be aligned with one edge of the photoconductive member, and only one side need be erased. When the electrophotographic printing machine is capable of varying the magnification of the copy, the size of the non-image areas change. For example, if a reduced size image is made, the interdocument area and one or both of the edge areas increase in size.
In order to erase the charged interdocument area, erase lamps extending across the photoconductive member perpendicular to the path of movement are energized for a selected time period as a function of the velocity of the photoconductive member so as to illuminate the entire interdocument area. The selected time of energization varies as a function of the size of the interdocument area. Edge erase requires that the length of the erase light be adjusted to compensate for different size images.
Various prior art charge erase devices are known and an extensive listing of references is identified and summarized in U.S. Pat. No. 4,806,975 (Godlove et al.), whose contents are hereby incorporated by reference. The Godlove patent discloses a multifunction plasma-erase lamp which incorporates a segmented electrode, each segment being selectively energized and associated with a specific erase function (interdocument, edge erase, formation of a test patch area). With the ever demanding customer requirement for improved copy quality and extended product life, it has become necessary to provide lamps with significantly improved light output stability, optimized spectral output and improved life characteristics. It has also become increasingly more important to utilize lamps capable of providing narrow exposure profiles necessitating narrow emitting areas and fast response times.